Mozilla squashes critical bugs in Firefox

Mozilla on Monday issued an update for Firefox that fixes four critical security bugs in the popular open-source browser, including one exposed last week that could make it easy for attackers to spoof SSL certificates used to secure websites.

The vulnerability meant Firefox could be tricked by rogue certificates, a potentially dangerous scenario that could allow attackers to create convincing-looking forgeries of websites used for banking, email and other sensitive services. The technique works by adding a simple null string character to several certificate fields and was independently reported at the Black Hat security conference by researchers Moxie Marlinspike and Dan Kaminsky.

The SSL vulnerability allowed Marlinspike to create what he called a universal wildcard certificate that caused Firefox to authenticate every domain name on the internet. He did so by applying for a normal certificate for his website thoughtcrime.org. In the commonName field he listed the site as *\0.thoughtcrime.org, causing the browser to believe the certificate was universally valid.

The vulnerability was repaired in version 3.5 of the browser, according to this catalog of security advisories. Curiously, the catalog shows the same hole being plugged in version 3.52, which was released Monday. Separate security advisories for 3.0 show it was also fixed in version 3.0.13.

Mozilla said three of its other products - Thunderbird, SeaMonkey and NSS - are vulnerable to the same attack. Presumably, fixes for those applications will be forthcoming.

The patch plugged other critical holes, including crashes that carried evidence of memory corruption, a heap overflow in certificate regexp parsing and a Chrome privilege escalation due to an incorrectly cached wrapper. Vulnerabilities rated critical typically allow an attacker to remotely execute malware on a vulnerable machine with minimal action needed on the part of the end user.

The patch brings the most recent version of Firefox to 3.5.2. For those who are unable to upgrade to version 3.5 of the browser, the open-source outfit issued a patch that brings the older version to 3.0.13. The vulnerabilities apply to the Windows, Mac and Linux platforms.

It's the second time in 18 days that Mozilla has fixed critical bugs in its flagship browser. Two weeks ago, the foundation rushed out a patch to repair a javascript-based memory corruption bug that was already being targeted in the wild.

Marlinspike said most internet client-side software that implements SSL are vulnerable to the null-string bug, so we'd expect this to be the first of many patches fixing that vulnerability. ®